nix-prisma-example VS nix-helpers

For the system, I like the devos template:

https://github.com/divnix/devos

The idea of flakes is how you define inputs, and you define the system (and packages, and shell etc.) in the outputs using the inputs. The inputs are git repos which point to other flakes. You can mix and match these as much as you want (see the devos repo for examples) and when you build the derivation, it generates a lockfile for exact commits in that point in time what were used in the given inputs.

You commit the lockfile and in the other systems where you pull your config from the repo, it uses exactly those commits and installs the same versions as you did in your other systems.

This was quite annoying and hard to do before flakes. Now it's easy.

The problem what people face with building their system as a flake is combining the packages so you can point to `jq` from the unstable nixos and firefox from the stable train. I think this aspect needs better documentation so it wouldn't be so damn hard to learn (believe me, I know). Luckily there are projects like devos that give a nice template for people to play with (with documentation!)

Another use for flakes is to create a development shell for your repo, an example what I did a while ago:

https://github.com/pimeys/nix-prisma-example

Either have `nix-direnv` installed, enter the directory and say `direnv allow`, or just `nix develop` and it will gather, compile and install the correct versions of packages to your shell. Updating the packages? Call `nix flake update` in the directory, commit the lockfile and everybody else gets the new versions to their shell.

Yes, to get Nixpkgs it's much faster to use `fetchTarball`.

You're right that `builtins.fetchTarball` is faster than `builtins.fetchGit` (due to the ridiculous amount of commits in the Nixpkgs repo). I like to keep such definitions in a single, company-wide/project-agnostic git repo (what the Nix Pills series calls the "repository pattern"), and have individual projects import them via `builtins.fetchGit`.

Many years ago we didn't have `builtins.fetchGit`, so had to use the 'fetchgit' function from Nixpkgs instead. That created a chicken-and-egg situation if we wanted to take the Nixpkgs version from some other git repo; hence needing to "bootstrap" via `(import { config = {}; }).fetchgit`, and cross our fingers that `NIX_PATH` wasn't set to some crazy value (which, of course, I would inevitably do... https://github.com/Warbo/haskell-te/blob/24475a229908caa3447... )

Note that we need `config = {};` when importing Nixpkgs to avoid an impurity which tries to read files in $HOME. More recent versions of Nixpkgs also need `overlays = [];` to avoid another impurity (looks like this changed at Nixpkgs 17.03, according to https://github.com/Warbo/nix-helpers/blob/master/nixpkgs.nix )

Where nixpkgs2105 is a pinned revision of the Nixpkgs repo, defined in another overlay. My current Nix config has pinned Nixpkgs versions going back to 2016. For example, here's a bunch of such overrides:

https://github.com/Warbo/nix-config/blob/master/overrides/fi...

At the moment I'm using niv to manage the pinned Nixpkgs versions (the 'repoXXXX' entries):

https://github.com/Warbo/nix-helpers/blob/master/nix/sources...